#region Copyright & License

//
// Copyright 2001-2005 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

#endregion

namespace log4net.Util {
  /// <summary>
  /// Implementation of Properties collection for the <see cref="log4net.GlobalContext"/>
  /// </summary>
  /// <remarks>
  /// <para>
  /// This class implements a properties collection that is thread safe and supports both
  /// storing properties and capturing a read only copy of the current propertied.
  /// </para>
  /// <para>
  /// This class is optimized to the scenario where the properties are read frequently
  /// and are modified infrequently.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  public sealed class GlobalContextProperties : ContextPropertiesBase {
    #region Private Instance Fields

    /// <summary>
    /// The read only copy of the properties.
    /// </summary>
    /// <remarks>
    /// <para>
    /// This variable is declared <c>volatile</c> to prevent the compiler and JIT from
    /// reordering reads and writes of this thread performed on different threads.
    /// </para>
    /// </remarks>
#if NETCF
		private ReadOnlyPropertiesDictionary m_readOnlyProperties = new ReadOnlyPropertiesDictionary();
#else
#endif

    /// <summary>
    /// Lock object used to synchronize updates within this instance
    /// </summary>
    readonly object m_syncRoot = new object();

    volatile ReadOnlyPropertiesDictionary m_readOnlyProperties = new ReadOnlyPropertiesDictionary();

    #endregion Private Instance Fields

    #region Public Instance Constructors

    /// <summary>
    /// Constructor
    /// </summary>
    /// <remarks>
    /// <para>
    /// Initializes a new instance of the <see cref="GlobalContextProperties" /> class.
    /// </para>
    /// </remarks>
    internal GlobalContextProperties() {}

    #endregion Public Instance Constructors

    #region Public Instance Properties

    /// <summary>
    /// Gets or sets the value of a property
    /// </summary>
    /// <value>
    /// The value for the property with the specified key
    /// </value>
    /// <remarks>
    /// <para>
    /// Reading the value for a key is faster than setting the value.
    /// When the value is written a new read only copy of 
    /// the properties is created.
    /// </para>
    /// </remarks>
    public override object this[string key] {
      get { return m_readOnlyProperties[key]; }
      set {
        lock (m_syncRoot) {
          var mutableProps = new PropertiesDictionary(m_readOnlyProperties);

          mutableProps[key] = value;

          m_readOnlyProperties = new ReadOnlyPropertiesDictionary(mutableProps);
        }
      }
    }

    #endregion Public Instance Properties

    #region Public Instance Methods

    /// <summary>
    /// Remove a property from the global context
    /// </summary>
    /// <param name="key">the key for the entry to remove</param>
    /// <remarks>
    /// <para>
    /// Removing an entry from the global context properties is relatively expensive compared
    /// with reading a value. 
    /// </para>
    /// </remarks>
    public void Remove(string key) {
      lock (m_syncRoot) {
        if (m_readOnlyProperties.Contains(key)) {
          var mutableProps = new PropertiesDictionary(m_readOnlyProperties);

          mutableProps.Remove(key);

          m_readOnlyProperties = new ReadOnlyPropertiesDictionary(mutableProps);
        }
      }
    }

    /// <summary>
    /// Clear the global context properties
    /// </summary>
    public void Clear() {
      lock (m_syncRoot) {
        m_readOnlyProperties = new ReadOnlyPropertiesDictionary();
      }
    }

    #endregion Public Instance Methods

    #region Internal Instance Methods

    /// <summary>
    /// Get a readonly immutable copy of the properties
    /// </summary>
    /// <returns>the current global context properties</returns>
    /// <remarks>
    /// <para>
    /// This implementation is fast because the GlobalContextProperties class
    /// stores a readonly copy of the properties.
    /// </para>
    /// </remarks>
    internal ReadOnlyPropertiesDictionary GetReadOnlyProperties() {
      return m_readOnlyProperties;
    }

    #endregion Internal Instance Methods
  }
}